1. Field
One or more embodiments relate to an organic light-emitting display device.
2. Description of the Related Art
An organic light-emitting display device includes a plurality of pixels that emit light to form an image. Each pixel includes a pixel circuit, an organic light-emitting diode, and an organic emission layer between two electrodes. The pixel circuit includes thin film transistors and a capacitor for driving the organic light-emitting diode. The transistors include a switching transistor and a driving transistor. In operation, electron and holes injected from the electrodes recombine in the organic emission layer to form excitons. Light is emitted when the excitons change state and release energy.
The gray scale value of light emitted from each pixel may be determined by adjusting the magnitude of a gate voltage Vgs of the driving transistor. The driving range of the driving transistor is based on the gate voltage Vgs, which is related to the channel length of a semiconductor layer of the driving transistor. The semiconductor layer may include polycrystalline silicon or amorphous silicon. Since the electron mobility of polycrystalline silicon is greater than that of amorphous silicon, polycrystalline silicon is generally used.
A polycrystalline silicon transistor has an off-current greater than that of an amorphous silicon transistor. In an attempt to compensate for the greater off-current of the polycrystalline silicon transistor, a lightly doped region may be arranged between heavily doped source and drain regions and a channel region of the polycrystalline silicon transistor.